BAGHDAD, Iraq (CNN) -- Fighting flared overnight in two key Shiite regions of Iraq, with four people killed early Wednesday in a U.S. airstrike in Basra and five others dying in battles in Baghdad's volatile northeastern region.

A woman sits outside her home while Iraqi soldiers search it in the Shiite city of Karbala on Wednesday.

Also, in Mosul, the U.S. military said Wednesday it killed a senior leader of al Qaeda in Iraq and accidentally shot and killed a bystander during a clash with militants.

In the Basra violence, the U.S. military said an unmanned aerial vehicle early Wednesday launched a Hellfire missile at five insurgents firing rocket-propelled grenades at Iraqi soldiers.

The Predator drone killed four "criminals" and wounded another in the Basra neighborhood Hayaniya -- a bastion of support for Shiite cleric Muqtada al-Sadr's Mehdi Army militia. Another missile was fired at the insurgents' vehicle, thought to contain weapons and ammunition.

"The message is clear to those that continue to obstruct the rule of law in Basra," said Capt. Chris Ford, spokesman for the coalition forces in Basra said in a statement. "Those attacking the Iraqi army and other government of Iraq security forces will be targeted as part of enduring coalition support to the people of Iraq."

A British military spokesman said there were no coalition casualties.

The strike comes during an Iraqi-led offensive in Basra targeting so-called "outlaws" in the city. Much of the fighting has involved security forces dominated by the Shiite party of the Islamic Supreme Council of Iraq fighting the Mehdi Army.

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The offensive, dubbed Charge of the Knights, commenced March 25 and the fighting set off intra-Shiite rivalries in Baghdad and Shiite cities in southern Iraq. The clashes died down a few days after they started when al-Sadr told his followers to lay down their weapons, but the offensive has continued.

Daily airstrikes and clashes have erupted every day for more than a week in northeastern Baghdad, including Sadr City -- the sprawling slum where the Mehdi Army holds sway.

In the latest fighting, two people were killed and 18 others wounded in Sadr City between 10 p.m. Tuesday and early morning Wednesday, an Interior Ministry official said. The official said the casualties were from airstrikes and battles.

The official said a mortar shell fell on a house along Palestine Street in northeastern Baghdad, killing at least three civilians killed and wounding four others from the same family.

The performance of the Iraqi army in the fighting across the Shiite regions has drawn both praise and scrutiny.

One issue that emerged in the Shiite region fighting was the poor performance of some of the Iraqi soldiers and police. The government fired 1,300 security forces in Basra and Kut for deserting their posts and laying down their arms.

The U.S. military confirmed a news report that a company of Iraqi soldiers retreated from their positions on Tuesday night in the Sadr City fighting and said the Baghdad Operations Command (BOC) will address the issue.

The report, in The New York Times, said the "retreat left a crucial stretch of road on the front lines undefended for hours and led to a tense series of exchanges between American soldiers and about 50 Iraqi troops who were fleeing." The report said the troops were eventually replaced by an "elite Iraqi unit."

"It is noteworthy the BOC was able to move another unit up," said Lt. Col. Steve Stover, a Multi-National Forces spokesman.

The fighting followed a day of violence in regions where Sunni militants have a strong presence.

Bombings thought to be conducted by al Qaeda in Iraq militants killed at least 60 people and wounded more than 100 people across Iraq on Tuesday. The incidents took place in Baghdad, in Ramadi in western Iraq, and in Diyala and Mosul in northern Iraq.

In Wednesday's fighting in Mosul, the U.S. military said the senior al Qaeda in Iraq leader and the bystander died as U.S. troops clashed with militants there.

Five other people were arrested in the incident, which began when insurgents shot at troops, which then returned fire, the military said.

"As the ground force called for occupants of one building to surrender, a man came out and refused to put down his pistol despite repeated warnings from coalition forces and an interpreter," a military statement said.

"The armed man demonstrated hostile intent, forcing coalition forces to engage him, subsequently killing the man. A woman who was standing directly behind the terrorist was also killed when rounds passed through him, striking and fatally wounding her."

The U.S. military also reported the arrests of "13 suspected terrorists" Tuesday and Wednesday during operations in the Tigris River Valley and northwest Iraq. The detentions were made during operations targeting al Qaeda in Iraq. E-mail to a friend